Motor vehicle manufacturers continue to study, improve and refine their products. Nearly every aspect of motor vehicle performance is under scrutiny. Passenger cars, sport utility vehicles and pickup trucks are significant objects of such study in areas of passenger comfort. One of the more esoteric areas under examination is cabin (passenger compartment) air infiltration and exfiltration. The flow of air into and out of the cabin affects not only noise levels and thus passenger comfort but also heating and cooling requirements. As permitted and average actual highway speeds again increase, proper understanding and quantitative analysis of air infiltration and exfiltration takes on added importance.
The infiltration/exfiltration of air during the forward motion of a xe2x80x9cclosedxe2x80x9d vehicle is an undesirable but natural phenomena associated with the non-uniform pressure values at the external surface of the vehicle and the numerous small openings between various passenger compartment components such as doors and door openings. Such infiltration and the corresponding exfiltration is the result of the relative motion between the vehicle and the surrounding air which creates positive pressure on the forward region of the vehicle and negative pressure over the remainder of the vehicle""s perimeter. Such positive and negative pressures exist with respect to the undisturbed ambient pressure.
Since the perimeter area that experiences negative pressure values is considerably larger than the area that experiences positive pressure, it can be expected that, in general, the passenger compartment will adopt a subatmospheric pressure condition at forward speeds.
The consequence of this is that the infiltration mass flow rate:                                                         m              .                                      i              ⁢                              xe2x80x83                            ⁢              n                                =                      "LeftBracketingBar"                                          ∫                                  A                                      i                    ⁢                                          xe2x80x83                                        ⁢                    n                                                              ⁢                              ρ                ⁢                                  xe2x80x83                                ⁢                                                      V                    →                                    ·                                      n                    ^                                                  ⁢                                  xe2x80x83                                ⁢                                  ⅆ                  A                                                      "RightBracketingBar"                          ,                            (        1        )            
will be non-zero. (By convention, {circumflex over (n)} is the outward drawn normal and, hence, the integral value is negative if the control surface surrounds the vehicle. The symbol xe2x80x9cAinxe2x80x9d represents the total of the infiltration areas.) The xcfx81 of equation (1) is that of the ambient air and, given the condition that Vvehicle/aambient less than 0.2 where a=the speed of sound in the ambient, the entering xcfx81 is safely assumed to be that of the atmosphere. In a steady state, the entering and exiting {dot over (m)} values are equal and this value ({dot over (m)}in) will be referred to as the xe2x80x9cinfiltration ratexe2x80x9d although it, of course, with equal accuracy quantitatively represents the exfiltration rate.
The fact that {dot over (m)}in is distributed over the forward region of the motor vehicle makes its direct assessment quite difficult. A stratagem to measure and determine such infiltration rate would therefore be highly desirable to assist in the analysis and improve performance and comfort of motor vehicles and similar structures such as unpressurized airplane cabins, train passenger cars and the like.
An apparatus and method for measuring the infiltration flow rate into the passenger compartment of a moving motor vehicle includes a controlled source of a gas such as carbon dioxide (CO2), a plurality of sensors disposed about the passenger compartment which provide data from which the concentration of such gas over time can be deduced and a multi-channel data storage device which discretely stores the concentration data from such plurality of sensors for later analysis and computation. The decay rate of the gas concentration within the passenger compartment is a function of the infiltration/exfiltration rate and the former rate can be deduced from the latter. Preferably, the vehicle will be stationary and disposed in a wind tunnel. However, testing with moving, remotely controlled vehicles on test tracks is also suitable. The apparatus and method have broad utility to determine infiltration/exfiltration rates of vehicular and non-vehicular compartments and containment structures such as unpressurized airplane cabins, train passenger cars, busses and the like subjected to an airstream.
Thus it is an object of the present invention to provide an apparatus for determining the infiltration/exfiltration rate of air into/out of a motor vehicle passenger compartment while in relative motion with respect to the approach air flow.
It is a further object of the present invention to provide a method of determining the infiltration/exfiltration of air into and or out of a motor vehicle passenger compartment while the vehicle is in motion.
It is a still further object of the present invention to provide an apparatus for measuring the concentration of a released quantity of a gas within a passenger compartment of a motor vehicle in actual or simulated motion to infer the infiltration/exfiltration rate.
It is a still further object of the present invention to provide a method for measuring the concentration of a released quantity of a gas within a passenger compartment of a motor vehicle in actual or simulated motion to infer the infiltration/exfiltration rate.
It is a still further object of the present invention to provide an apparatus for determining the infiltration/exfiltration rate of a compartment or containment structure subjected to an airstream.
It is a still further object of the present invention to provide a method for determining the infiltration/exfiltration rate of a compartment or containment structure subjected to an airstream.
Further objects and advantages of the present invention will become apparent by reference to the following description of the preferred embodiment and appended drawings wherein like reference numbers refer to the same assembly, element, component or feature.